Drill bit mechanism



March 17, 1959 w. E. C LAVlER ETAL 2,

DRILL BIT MECHANISM v 2 Sheets-Sheet 1 Filed June 4, 1957 2'INVENT0RS WILLIAM E. CLAVIE-R BY GEORGE H. EATON E YMONDEBENIGHT 4 Af-Z-y's.

March 17, 1959 w. E. cLAvlER ETAL 2,877,986

DRILL BIT MECHANISM 2 Sheets-Sheet 2 Filed June 4, 1957 INVENTORS WILLIAM E. CLAVIER GEORGE H. EATON BY AYMONDEBENIGHT AIH s.

DRILL BIT MECHANISM William E. Clavier, Portland, and George H. Eaton,-

gezli verton, reg., and Raymond F. Benight, San Jose,

Application June 4, 1957, Serial No. 663,476

15 Claims. (Cl. 255-61) This invention relates to drilling mechanism and more particularly to a novel power-driven bit construction for drilling gear such as may be used for the exploration or production of minerals, oil, gas, water, and the like. The construction and organization of the bit and associated mechanism are characterized by a number of novel features contributing tothe usefulness and efficiency of the 7 bit.

Generally, it is an object of this invention to provide, for powered drilling apparatus, a power-driven sectional bit mechanism for cutting into the ground wherein the sections of the bit are mounted for pivotal movement in the housing for the tool, the cutting edges carried by the sections moving in a bore upon actuation of the bit mechanism both laterally and longitudinally of the bore.

Another object .of this invention is to provide a powerdriven sectional bit mechanism for drilling tools wherein pivotal movement of the bit sections causes head portions which carry the cutting edges of the bits to travel from an aligned position, wherein the cutting edges are positioned side by side, to a misaligned position, wherein the cutting edges of one bit section protrude outwardly and overlap the cutting edges of the other bit. section. In this way, expansion of the over-all width of the bit mechanism may be produced whereby'etfective impact or shatter blows. are delivered to the sides of a bore. Further, reciprocal movement of a tool longitudinally of a bore may be produced, valuable in disintegrating the of the drill stem, inefficient penetration of various, earth 1 strata, bearing failure, excessive bit wear, an inability to transmit efliciently the work developed by the motor means for the tool into cutting work performed onthe bottom or sides of a well bore, etc.

To overcome these and other difficulties, the bit construction herein contemplated employs a sectional bit or cutting mechanism carried at the base of the drilling tool wherein the sections of the cutting mechanism move back and forth transversely of the well bore in progressing downwardly through the bore. The sections each have a curved contact surface which carries the cutting teeth for the section. Each of the sections is pivoted about an axis spaced from the radial center for the curvature of the contact surface. In this way, pivotal movement of the bit sections produces a rotary and a sweeping movement in the cutting edges which erodes away the various strata encountered by the tool. In other words, a combined chipping or slicing and penetrating or percussion stroke occurs in each section of the bit mechanism when it is pivoted about its pivot axis.

Patented Mar. 1'7, 1959 p The bit sections or members of this invention each include a lever arm portion which is connected to the motor driving the drilling tool whereby actuation of the motor serves to impart pivotal movement to the bit members. By using the lever principle in the mechanism connecting the bits to the drilling tool motor, an effective transfer of the power delivered by the motor to the bit sections is created. Also, a mechanical advantage may be introduced between the motor and the cutting edges of the bit sections.

motion are of the bits may be constructed so that misalignment of the bits occurs for the most part along the bottom or base of the bitmembers, such misalignment functioning to produce reciprocal movement in the tool longitudinally of a well bore. On the other hand, the motion are of the bit members may be constructed so 'that misalignment occurs for the most part along the sides of the bit members. In this instance, an expansion of the over-all width occupied by the bit members is created so that positive impact blows are delivered laterally to the sides of a well bore. In this case, reaction forces take place substantially transversely of the well bore. A combinationof these two types of movement is also possible.

Further, the misalignment of the head portions for the bit members may be created when the lateral edges of the head-portions are sweeping either downwardly or upwardly relative to the sides of a well bore.

y Thus, an opportunity is presented for varying the type of misalignment, depending upon the particular type of drilling operation.

A more specific object of the invention, therefore, is to provide, for a well drilling tool, a bit construction employing bit members pivotally mounted at the base of the tool wherein the cutting edges of the bit members are carried on a curved contact surface, and the bit members are pivoted about an axis spaced from the radial center for the curvature for the contact surface whereby the cutting edges are moved with a rotary and a sweeping movement in progressing downwardly in a well bore.

A further object of the invention is to provide, for a well drilling tool, a bit construction employing a pair of pivotally mounted bit members, each'of the bit members having head portions which are allochiral, wherein pivotal movement of the bit members moves the head portions out of alignment to produce an expansion in the over-all width occupied by the bit members and/ or reciprocal movement of the tool longitudinally of a well bore.

These and other objects and advantages are attained by the present invention, various novel features of which will become more fully apparent when the following description is read in conjunction with the accompanying draw ings wherein:

' Fig. 1 is a sectional view of the lower end of a drilling tool, showing a portion of the housing for the tool and a sectional bit mechanism carried at the lower end of the housing;

Fig. 2 is an end view, partly simplified for reasons of clarity, of the drilling tool inFig. 1;

Fig. 3 is a side view, partly in section, illustrating a modified form of the bit mechanism of this invention;

Fig. 4 is another side view, partly in section, of the mechanism illustrated in Fig. 3; v

Fig. 5 is a section view along the line 5-;5 in -Fig. 3;

I and Figs. 6a, 6b, and 60 through Figs. 10a, 10b, and 10c are schematic showings, illustrating the movement of the bit elements of this invention about various pivot axes.

This application is a continuation, in part, of the application of Clavier et aL, entitled Drilling Equipment, filed September 28, 1956, Serial No. 613,476.

Referring now to the drawings wherein various embodiments of this invention are illustrated, and more particularly to Figs 1 and 2, 10 indicates generally the housing for a well drilling tool. In the embodiment shown in Fig. l, the housing comprises an upper tubular section 11, a lower tubular section 12, and a cap section 13. These various segments are atfixed together in any suitable manner, as by threaded portions presented at appropriate ends of the segments.

Extending through the interior of housing 10, with its lower end pivoted at 14 to a pair of links .16 and 17, is a rod 18. Rod 18 extends upwardly Within the housing and is connected at its upper end to a motor (not shown) which imparts reciprocal movement to the rod. The motor may be conventional and forms no part of this invention. Exemplary of a type of motor which may be employed is that shown in the copending application of Clavier et al., entitled Drilling Equipment, Serial No. 613,476.

Pivoted to a pair of lug portions 23, 24 carried by cap section 13 at the lower end of the drilling tool is a sectional bit mechanism comprising a pair of bit members 26 and 27. The bit members are pivoted to the lug portions as by pivot pin 28 extending through the bit members intermediate their ends. The bit members are aflixed to the lug portions by nuts 29, 31 threaded onto the ends of pin 28.

The lower end of each of the bit members has integrally formed therewith a cutting head portion, indicated ,at 32 and 33, respectively. In Fig. 1, head portion 32 has been removed and is shown by dotted outline only. ,As illustrated in the drawings, these cutting head portions are allochiral. Each cutting head conforms generally to a segment of a sphere, the outer dimension of the head portions being substantially the same and the two head portions complementing each other. When the two head portions are mutually aligned, their peripheral outlines match with each other to define a continuous spherical outline.

The curved outer surface of each head portion, which constitutes a contact surface for the bit member, carries a series of cutting edges'or teeth 34. The teeth serve as the abrading means for the bit members.

Lever arms 41 and 42, affixed to head portions 32 and 33, respectively, extend upwardly and are connected to links 16 and 17 by pivot connections 43 and 44. The pivotable scissor connection between the piston rod 18 and lever arms 41, 42, supplied by links 16, 17 enables pivot l movement of bit mem ers 26, .27 to be produced in response to reciprocal movement of rod 18. This pivotal movement of the bit members, in turn, produces to-and-fro movement of the cutting or abrading edges of the bit members in arcs extending substantially transversely of the well bore.

Attention is drawn to the. fact that the radial center of curvature for the outer or contact surface of each head portion, indicated at points 36 and 37, is located downwardly from the center of pivot pin28. which is indicated at 38. In Fig. l, the head portions are spread apart from each other, or misaligned, with the outer edges of one overlapping the outer edges of the other. Pivotal movement of the bit members by downward movement of rod 18 causes the head portions to move to an aligned position indicated by the dotted lines in Fig. 2. In this condition of the parts, radial centers 36 and 37 align with each other since the head portions complement each other as described hereinabove. The radial centers of the head portions then lie in a vertical plane passing through center 38 of pivot pin 28. The location of pivot pin v28 away from the radial centers of the cutting heads causes the teeth carried by each cutting head to partially revolve and partially sweep across an obstruction when they are set in motion by pivotal movement of the bit members. Thus, a unique combination of a chipping or slicing stroke coupled with a percussion type of stroke is produced. Also, in moving from an aligned to a misaligned position, expansion of the over-all width of the cutting head portions and/or reciprocal movement of the tool may be produced, as will be discussed hereinbelow.

It should be understood that pivotal movement of the bit members may be produced in any number of ways. In the embodiment illustrated in Figs. 1 and 2, pivotal movement is produced by reciprocal motion of rod 18. This reciprocal motion, in turn, is brought about by a suitable motor means carried in the housing at the upper end of the tool. Pivotal movement of the bit members may also be produced by a rotary shaft in the manner described in connection with the embodiment illustrated in Figs. 3, 4, and 5.

Referring to Figs. 3, 4, and .5, in the embodiment of the invention illustrated, a pair of bit members 51, 52 are pivotally mounted in lug portions 49, 50 of housing 10 for pivotal movement about separate pivot axes which are spaced from each other. Each bit member is mounted by a separate pivot pin, indicated at 53 and 54, respectively, to one of the lug portions. Each pivot pin may be rotatably mounted in 2. lug portion as by bushing 56 and fastened as by screws threads to lever arms 57, 58 of the bit members.

..As in the case of the embodiment shown in Figs. 1 and 2, bit membersSl and 52 have complementary head portions 60 and 61 curved about radial centers and carrying teeth 64. In Fig. 3, the head portions of the bits are mutually aligned so that the radial centers for the head portions are aligned at a point indicated at'65. The head portions are moved out of alignment bypivotal movement of arms 57 and 58 about pins 53, 54. Since the pivot axes for the bit members do not coincide with the radial centers for the head portions of the bit members, the teeth of the head portions partially revolve and partially sweep across obstructions encountered by the tool.

In the embodiment of Figs. 3-5, pivotal movement of the bit members is produced by a rotary shaft 66 which is driven by a conventional motor carried at the top of the housing for the tool. Specifically, lever arms 57 and 58 of the bit elements project upwardly within the interior of housing 10. Each of the arms is provided at its upper end with a ball portion 67. Each of the ball portions is seated in a cavity 68 formed in the outer extremities of a cam member 69. Each cam member rotatably and slidably seats on an eccentric 71 secured to shaft 66. ,As can best be seen in Fig. 5, eccentric 71 rides about an inner race 72 of cam :member 69. By this construction, rotary movement of shaft 66 operates to urge ball portion 68 of each arm toward and away from the housing 10, thereby to produce pivotal movement of the bit members. Lever arms 57, 58 of the bit members move outwardly and inwardly from the position shown for the arms in Fig. 3 so that the head portions carried by the arms are moved to either side of the aligned position illustrated in Fig. 3.

Generally, this invention contemplates mounting the bit members so that the cutting head portions of the members pass from an aligned position to a misaligned position wherein edge portions of one of the cutting heads protrudes over or overlaps edge portions of the other cutting head. The pivot connection for the bit members may be selected to produce predominantly misalignment of the lateral edges of the cutting heads. Alternatively, misalignment may be produced predominantly along the lower edges of the cutting heads whereby a vertical percussion-type stroke is produced in the tool. Still further, a c m ination of th t yp s of movement is p ssi l In addition, it is possible "to select whether lateral miss alignment is achieved by a motion are of the cutting head moving either upwardly or downwardly relative to the sides of a well bore.

Referring to Figs. 6a, 6b, and 60 through Figs. a, 10b, and 100, movement of the cutting heads according to this invention is illustrated diagrammatically. The figures illustrates a few of the types of movement possible for different relative positioning of the pivot axes for the bit members and the radial centers for the cutting heads. In the discussion, it should be understood that the structure of the bit members and associated mechanism for driving the members may conform to the structure illustrated in Figs. 15. Obviously, other types of construction are also possible, and it is not intended to be limited by the specific showing of Figs. 1-5. In the figures, the dotted outlines indicate the positions of a cutting head when it is positioned upright in a well bore, and the solid outlines indicate the positions of a cutting head after it has been pivoted about its pivot axis away from its upright position.

Referring to Figs. 6a, 6b, and 6c, 71 indicates the radial center of a cutting head and 72 indicates the pivot axis for the cutting head. It will be noted that the pivot axis for the cutting head is located in a vertical plane passing through the radial center of the cutting head when the bit is vertically positioned in a bore but below the radial center for the cutting head. Pivotal movement of the cutting head in a counterclockwise direction about pivot axis 72 causes left hand edge portions of the cutting head to move outwardly and downwardly and right hand edge portions of the cutting head to move inwardly and upwardly, as indicated by the arrows. The lower edge portions of the bit remain substantially at the same level. This type of motion results, as can be seen with reference to Fig. 6b, since movement of radial center 71 occurs for the most part in a direction normal to the outer lateral edges of the cutting head and a direction roughly parallel to the bottom edges of the cutting head. Referring to Fig. 6c, pivotal movement of the cutting head in a clockwise direction about axis 72 causes right hand edge portions of the cutting head to move outwardly and downwardly and left hand edge portions of the cutting head to move upwardly and inwardly. Again the lower edge portions of the cutting head remain substantially at the same level. When two cutting heads are employed, each pivoted about an axis positioned in the manner shown in Figs. 6a-6c, but in opposite directions, pivotal movement of the cutting heads causes the lateral edges of the cutting heads to alternate with each other in protruding outwardly to either side of a well bore. Further, the lateral edges, in moving outwardly, are also moving downwardly in the well bore. The cutting heads, in moving to a misaligned position, cause an expansion to take place in the over-all width occupied by the cutting heads. The expansion takes place transversely across the width of the well bore. The reaction force set up when one of the bit sections engages one side of a well bore is delivered transversely across the well bore to the other bit section engaging the opposite side of the well bore.

Referring to Figs. 8a-8c, in this instance the radial center of a cutting head is indicated at 76, and the pivot axis for the cutting head is indicated at 77. In this embodiment, the pivot connection is located in a vertical plane passing through the radial center of the cutting head when the cutting head occupies its upright position above the radial center for the cutting head. This type of pivot connection for a cutting head is incorporated in the embodiment discussed in connection with Figs. 1 and 2. Referring now to Figs. 8b and 8c, movement of the cutting head in a counterclockwise direction about pivot connection 77 causes right hand edge portions of the cutting head to move outwardly and upwardly into the sides of a well bore and left band edge portions of the cutting head to move downwardly and inwardly. Movement of the cutting head in a clockwise direction about pivot connection 77 results in right hand edge portions of the cutting head moving inwardly and downwardly and left hand edge portions of the cutting head moving outwardly and upwardly. In this instance, as in the embodiment illustrated in Figs. 6a-6c, bottom edge portions of the cutting head remain at approximately the same level due to the fact that radial center 77 moves in a direction roughly parallel to the bottom edges of the cutting head. When a pair of cutting elements are employed, and each is pivoted in opposite directions, lateral edges of the cutting heads alternate with each other in protruding outwardly to either side of a well bore. However, the lateral edges, in moving, are also moving upwardly as compared to the showing in Figs. 6a-6c where the lateral edges are moving downwardly.

In Figs. 7a7c, the pivot axis for a cutting head is indicated at 81, and the radial center for the cutting head is indicated at 82. In this instance, the pivot connection for the cutting head is located on a horizontal plane passing through the radial center of the cutting head when the cutting head occupies its upright position but to the left of the radial center. Referring to Figs. 7b and 7c, rotation of the cutting head in a counterclockwise direction upon its pivot connection causes the lower edges of the cutting head to be retracted upwardly and to the right. When the cutting head is pivoted in the other direction, the lower edges of the cutting head move downwardly and to the left. There is substantially no lateral shifting of lateral edge portions of the cutting head. When a pair of cutting heads are employed, pivotal movement of the cutting heads in opposed directions causes lower edge portions of the cutting heads to alternate with each other in protruding downwardly into the end of a well bore. This produces reciprocal movement in a tool longitudinally of a well bore, valuable in cutting into rock formation.

Referring to Figs. 9a-9c, the pivot axis for a cutting head is indicated at 86 and the radial center for the cutting head at 87. The pivot connection illustrated in these figures has been located upwardly and to the right of the radial center or the cutting head when the cutting head occupies its upright position. When a pair of cutting heads are used, pivotal movement of the cutting heads about pivot connection 86 in opposite directions causes a combination of the longitudinal reciprocal'stroke discussed in connection with Figs. 7a-7c and the lateral expansion stroke discussed in connection with Figs. 8a-8c. If the pivot connection is placed downwardly and either to the right or left of the radial center, the longitudinal reciprocal stroke discussed in connection with Figs. 7a-7c results as well as the expansion stroke discussed in connection with Figs. 6a-6c.

In Figs. lOa-lOc, an embodiment is illustrated wherein one cutting head 89 is pivoted about a pivot axis 91 spaced laterally to the right of its radial center 93, and another cutting head is pivoted about pivot axis 92 spaced laterally to the left of its radial center 94 when the cutting heads occupy an upright position. If the cutting heads are pivoted in opposite directions, bottom edge portions of the cutting heads remain substantially aligned. However, they first retract and then protrude, in unison, from the position they occupy in a well bore when the cutting heads occupy an upright position. movement imparts a longitudinal reciprocal stroke to a. drilling tool. the figures, that lateral edge portions of the cutting heads alternate with each other in protruding outwardly to either side of a well bore. This produces a lateral expan sion stroke in the tool. The arrangement of the cutting heads and pivot axes in Figs. l0a-10c is similar to the embodiment discussed in connection with Figs. 3-5.

In summary, it will be noted that a number of novel advantages may be obtained employing the constructions of this invention.

This

Further, it will be noted from observing Movement of the cutting heads of the. bit members produces a rotary as well as a sweeping move- 7 ment of the cutting edges carried by the cutting heads. This results in a chipping or slicing stroke coupled with a percussion stroke. Further, an expansion in the overall width occupied by the cutting heads may be obtained which is highly effective. Also, reciprocal movement of the tool longitudinally of a well bore is possible.

By oifsetting the pivot axis or axes of the bit members from the radial center of the contact surface, a wide selection of bit performances can be realized. The amount of offset and the angle of offset determines the type of percussion and chipping stroke obtained.

While there has been described a few embodiments of this invention, it is not intended to be limited thereby, and it is desired to cover all modifications which would be apparent to one skilled in the art and that come within the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. In a drilling tool, said tool having a housing portion and motor means driving the tool, a sectional cutting mechanism comprised of at least two sections pivotally connected for movement in parallel planes to the lower end of said housing portion for cutting obstructions en countered by said tool, each section having a cutting head at its lower end which includes a bottom cutting surface extending between right and left sides of the cutting head viewing the head transversely of its plane of movement, each section of said cutting mechanism pivoting about a pivot connection fixed to said housing portion, and means connecting each section to said motor means whereby the sections are pivoted to-and-fro in opposed direc tions upon actuation of said motor means, the cutting surface of the cutting head for each section being spaced closer to the pivot connection for the section on one side of the cutting head than the cutting surface on the other side of the cutting head, the pivot connections for the sections mounting the sections so that their cutting surfaces alternate with each other in protruding downwardly into a bore upon pivotal movement of the sections, whereby pivotal movement of the sections produces reciprocal movement of the total longitudinally of a bore formed by the tool.

2. In a drilling tool, said tool having a housing portion and motor means driving the tool, a sectional cutting mechanism comprised of at least two sections pivotally connected for movement in parallel planes to the lower end of said housing portion for cutting obstructions encountered by said tool, each section having a cutting head at its lower end which includes a bottom cutting surface of curved peripheral outline extending between right and left sides of the cutting head viewing the head transversely of its plane of movement, the cutting heads for the two sections having substantially the same width, each section of said cutting mechanism pivoting about a pivot connection fixed to said housing portion, and means connecting each section to said motor means whereby the sections are pivoted to-and-fro upon actuation of said motor means, the pivot connections for the sections mounting the sections so that their cutting surfaces alternate with each other in protruding outwardly to either side of a bore upon pivotal movement of the sections, thereby to produce expansion of the cutting mechanism laterally against the sides of a bore formed by the tool.

3'. In a drilling tool, said tool having a housing portion and motor means driving the tool, a pair of bit members pivotally carried by said housing portion for pivotal movement in parallel planes at the lower end thereof for cutting obstructions encountered by the tool, each of said bit members having a cutting head portion at the lower end thereof, each cutting head portion hav ing a cutting surface extending along the base and sides of the head portion viewing the head portion transversely of its plane of movement, the cutting head portions of the two bit members being allochiral and of substantially the same size, and means connecting each bit member to 8 said motor means whereby the members are pivoted toand-fro in opposite directions by actuation of said motor means, said bit members pivoting about pivot connections mounting the bit members during a portion of their move ment with their cutting head portions substantially in an aligned position, each of said bit members pivoting about an axis spaced a nonuniform distance from the peripheral outline of the cutting surface for the member, said bit members pivoting so that they ride past a position wherein the cutting head portions of the bit members are mutually aligned with each other, to misaligned positions wherein said cutting head portions are out of alignment.

4. In a drilling tool, said tool having a housing portion and motor means driving the tool, a pair of bit members pivotally mounted adjacent one another for movement in parallel planes at the lower end of said housing portion for cutting obstructions encountered by the tool, each of said bit members having a cutting head portion at the lower end thereof, each cutting head portion having a cutting surface extending along the base of the head portion between right and left sides of the head portion viewing it transversely of its plane of movement, the cutting head portions of the bit members being allochiral and of substantially the same size, and means connecting the bit members to said motor means whereby the bit members are pivoted to-and-fro in opposed directions by actuation of said motor means, the cutting surface of the cutting head portion for each section being spaced closer to the pivot connection for the section on one side of the cutting head portion than the cutting surface on the other side of the cutting head portion, said bit members pivoting so that the cutting surfaces of the head portions for the bit members alternate with each other in protruding downwardly into a bore, whereby pivotal movement of the bit members produces reciprocal movement of the tool longitudinally of a bore formed by the tool.

5. In a drilling tool, said tool having a housing portion and motor means driving the tool, a pair of bit members pivotally mounted adjacent one another at the lower end of said housing portion for cutting obstructions encountered by the tool, said bit members pivoting in parallel planes each of said bit members having a cutting head portion at the lower end thereof, each cutting head portion having a cutting surface of curved peripheral outline extending along the base and sides of the cutting head portion viewing the head portion transversely of its plane of movement, the cutting head portions of the two bit members being allochiral and of substantially the same size, and means connecting the bit members to said motor means whereby the bit members are pivoted to-and-fro in opposed directions by actuation of said motor means, said bit members pivoting about pivot connections mounting the bit members during part of their movement with their cutting head portions in an aligned position, the pivot axes for said bit members being spaced substantially centrally between the cutting surfaces along the sides of the cutting head portions for the bit membersand spaced from the cutting surfaces along the base of the cutting head portions a distance different from the spacing from the cutting surfaces along the sides of the head portions.

6. In a well drilling tool for drilling well bores, said tool having a housing portion and motor means mounted in said housing portion, a pair of bit members, a cutting head portion for each of said bit members, each cutting head portion having a contact surface carrying a series of cutting edges, pivot means fixed to said housing portion mounting said bit members adjacent one another for pivotal movement relative to each other in parallel planes, and means connecting each of said bit members to said motor means to be pivoted to-andfro by actuation of said motor means, the cutting head portions for they hit members being allochiral and of substantially the. same size portion, said pivot means mounting said bit members during a portion of their movement with their cutting head portions in substantially an aligned position, the bit members pivotii: g about axes spaced a nonuniform distance from the peripheral outline of the base and sides of said cutting head portions viewing the head portions transversely of their plane of movement whereby the head portions move from an aligned position to positions which are out of alignment.

7. In a well drilling tool for drilling well bores, said tool having a housing portion and motor means mounted in said housing portion, a pair of bit members, a cutting head portion for each of said bit members, the cutting head portions for the bit members being allochiral and of the same size, each cutting head portion having a contact surface carrying a series of cutting edges, pivot means fixed to said housing portion mounting said bit members adjacent one another for pivotal movement in parallel planes, each bit member having an arm portion fixed to the cutting head portion for the member, and means connecting each arm portion to the motor means for said tool whereby the bit members are pivoted toand-fro by actuation of said motor means, the pivot means for the bit members mounting the bit members for movement of their head portions into an aligned position, the pivot axis for each bit member being closer to the contact surface along one side of the cutting head portion for the bit member than the contact surface along the other side of the cutting head portion viewing the cutting head portion transversely of its plane of movement.

8. In a well drilling tool for drilling well bores, said tool having a housing portion and motor means mounted in said housing portion, a pair of bit members, a cutting head portion for each of said bit members, each cutting head portion having a contact surface carrying a series of cutting edges, pivot means fixed to said housing portion mounting said bit members adjacent one another for pivotal movement in parallel planes, each bit member having an arm portion fixed to the cutting head portion for the member, and means connecting each arm portion to the motor means for said tool whereby the bit members are pivoted to-and-fro by actuation of said motor means, each cutting head portion having a substantially symmetrical shape defined relative to a symmetrical center line for the cutting head portion viewing the head portion perpendicularly of its plane of movement, the two cutting head portions having substantially the same size and shape, the pivot means for the bit members mounting the cutting head portions of the bit members during a portion of their movement with the sides of the cutting head portions substantially mutually aligned, the pivot axis for each bit member being spaced centrally of the sides of the cutting head portion for the member viewing the bit member perpendicularly of its plane of movement and spaced from the base of the cutting head portion a distance different from the spacing between the two sides.

9. In a well drilling tool for drilling well bores, said tool having a housing portion and motor means within said housing portion, power-driven cutting mechanism for said tool at the lower end thereof comprising a pair of bit members, a head portion for each of said bit members, each head portion having a contact surface at the lower end of the bit member carrying a series of cutting edges, the peripheral outline of the contact surface of each head portion curving about a radial center, pivot means fixed to said housing portion mounting said bit members adjacent one another for pivotal movement relative to each other, and an arm portion for each of said bit members fixed to the head portion for the bit member and connected to said motor means, actuation of said motor means pivoting said bit members to-andfro in opposed directions, said pivot means mounting each of said bit members for pivotal movement on an axis spaced from the radial center for the head portion 10 of the bit member, the head portion of one of said bit members having the same outer dimension and complementing the head portion of the other'of said bit members, pivotal movement of the bit members moving the head portions from a mutually aligned position to a misaligned position.

10. In a well drilling tool for drilling well bores, said tool having a housing portion and motor means within said housing portion, power-driven cutting mechanism for said tool at the lower end thereof comprising a pair of bit members, a head portion for each of said bit members, each head portion having a contact surface at the lower end of the bit member carrying a series of cutting edges, the peripheral outline of the contact surface of each head portion curving about a radial center, pivot means fixed to said housing portion mounting said bit members adjacent one another for pivotal movement relative to each other about a common axis, and an arm portion for each of said bit members fixed to the head portion for the bit member and connected to said motor means, actuation of said motor means pivoting said bit members to-and-fro in opposed directions, said bit members pivoting about a common axis which is spaced from the radial centers for the head portions of the bit members, the head portion of one of said bit members having the same outer dimension and complementing the head portion of the other of said bit members, pivotal movement of the bit members moving the head portions from a mutually aligned position to a misaligned position.

11. The device of claim 10 wherein the bit members are pivoted on a common axis spaced on a vertical plane passing through the radial centers for the head portions of the bit members when the bit members are aligned so that misalignment of the bit members caused by pivotal movement of the bit members occurs laterally to either side of the members.

12. The device of claim 10 wherein the bit members are pivoted on a common axis spaced laterally to one side of the radial centers for the head portions of the bit members when the bit members are aligned so that misalignment of the bit members caused by pivotal movement of the bit members occurs at the base of the bit members.

13. A bit for a well drilling tool comprising an arm portion and a head portion fixed to the lower end of said arm portion, and means for pivotally mounting the bit intermediate the ends thereof, said head portion conforming substantially to a segment of a sphere and having a contact surface whose peripheral outline is curved about a radial center, said contact surface carrying a series of cutting edges, said means for pivotally mounting said bit being spaced away from the radial center for the head portion of said bit.

14. In a well drilling tool for drilling Well bores, said tool having a housing portion and motor means within said housing portion, power-driven cutting mechanism for said tool at the lower end thereof comprising a pair of bit members, each of said bit members having an arm portion and a head portion fixed to the lower end of said arm portion, said head portion conforming substantially to a segment of a sphere and having a contact surface whose peripheral outline is curved about a radial center, said contact surface carrying a series of cutting edges, and means pivotally mounting said bit members for movement about a pivot axis spaced from the radial center for the head portions of the bit members, actuation of said motor means pivoting said bit members.

15. In a well drilling tool for drilling well bores, said tool having a housing portion and motor means within said housing portion, power-driven cutting mechanism for said tool at the lower end thereof comprising a pair of bit members, a head portion for each of said bit members, each head portion having a contact surface at the lower end of the bit member carrying a series of cutting edges,

the peripheral outline of the contact surface of each head of said bit members for pivotal movement about an axis portion curving about aradial center, pivot means fixed to spaced from the radial center for the head portion of said housing portion mounting said bit members adjacent the bit member. one another for pivotal movement relative to each other, and an arm portion for each of said bit members fixed '5 References Cited 1!! the 516 of {1113 Patent to the head portion for the bit member and connected to UNITED STATES PATENTS said motor means actuation of said motor means pivot- 463,880 Webber Nov. 24, 1891 mg said bit members, said plvot means mounting each 471,580 Webb Man 29 1892 

